.beta.-receptor blocking agents such as propranolol, ##STR3## alprenolol, ##STR4## and metoprolol, ##STR5## have been shown to possess good therapeutic effects in treating heart diseases and vascular diseases, such as angina pectoris, hypertonia, vasoregulatorial neurasthenia and certain forms of arrhythmia.
The pharmacologically active form of the above-mentioned and other .beta.-receptor active agents have the S configuration, and methods for the synthesis of such compounds in enantiomerically pure form are clearly valuable.
Of the various methods available for the synthesis of individual enantiomers, some are based upon the use of optically active natural products such as carbohydrates. In the case of the above-mentioned B-receptor active agents, methods for their synthesis from the naturally occuring alditol, D-mannitol, have been described e.g. in GB 1 598 667 and GB 1 598 668. All these methods start with cleavage of the C.sup.3 -C.sup.4 -bond of 1,2:5,6-di-O-isopropylidene-D-mannitol with periodate or lead tetraacetate. The isopropylidene-protected D-glyceraldehyde is, however, an unstable compound that rapidly undergoes decomposition. Its water solubility poses additional problems in the isolation.